As an apparatus for suppressing vibration noise in the passenger compartment, an active noise control apparatus (hereinafter referred to as “ANC apparatus”) has been known. Further, as an apparatus for suppressing vibration itself or vibration noise in the vehicle interior, an active vibration control apparatus (hereinafter referred to as “AVC apparatus”) has been known.
In a general ANC apparatus, the target noise is reduced by outputting from the speaker in the vehicle interior an antiphase canceling sound with respect to the target noise. The error between the target noise and the canceling sound is detected as residual noise by a microphone disposed in the vicinity of the ear of the occupant, and is used for subsequent determination of canceling sound. The ANC apparatus may reduce, for example, vehicle interior noise (engine muffled sound) in response to engine vibration or vehicle interior noise (road noise) caused by the wheels of a moving vehicle in contact with the road surface (see, for example, Japanese Laid-Open Patent Publication No. 07-104767 (hereinafter referred to as “JP 07-104767 A”) and U.S. Patent Application Publication No. 2009/0060217 (hereinafter referred to as “US 2009/0060217 A1”) reference).
In a general AVC apparatus, vibration generated in opposite phase to the target vibration is generated by an actuator, thereby reducing the target vibrations transmitted to the vehicle interior. The error between the target vibration and the canceling vibration is detected as a residual vibration by a vibration sensor disposed in the vicinity of the actuator, and it is used to determine subsequent canceling vibration. For example, the AVC apparatus suppresses transmission of engine vibration to the vehicle interior (see, for example, U.S. Patent Application Publication No. 2012/0032619 (hereinafter referred to as “US 2012/0032619 A1”)).
In JP 07-104767 A and US 2009/0060217 A1, an adaptive control is used to generate a canceling sound. More specifically, in JP 07-104767 A, the first basic signal X1 based on the engine speed [rpm] is multiplied by the filter weight Wim in the first adaptive filter group 32 to generate the speaker drive signal Yim (FIG. 1, [0018]). As a result, the engine noise is reduced. The filter weight Wim is calculated based on the first basic signal X1 and the detection signal e1 from the microphone 40 ((0021)). Further, similar controls are also carried out for road noise (vibration detected by the input vibration detection unit 18) and wind noise (sound pressure detected by the input sound pressure detection unit 24) ([0022]).
Also, in US 2009/0060217 A1, the first basic signal generator 31 generates a first basic signal Sr1 synchronized with the road noise frequency fd (FIG. 1, [0042]). The first adaptive filter 36 generates a first control signal SC1 from the first basic signal Sr1 (FIG. 1, [0042]). The filter coefficient W1 used in the first adaptive filter 36 is set by the filter coefficient updating unit 38 ([0042], [0043]).
The filter coefficient updating unit 38 calculates the filter coefficient W1 based on the reference signal r from the reference signal generation unit 34, the error signal ea from the microphone 22, etc. ([0042]). The reference signal generation unit 34 calculates the reference signal r based on the simulated transfer characteristic C^([0042]).
In US 2012/0032619 A1, the canceling vibration is generated using an adaptive control. Specifically, the frequency identifying unit 83a (FIG. 6) identifies the frequency of engine vibration in the vibration mode of the maximum amplitude based on the TDC pulse signal and the CRK pulse signal ([0120]). The basic signal generation unit 83b generates a basic signal based on the frequency identified by the frequency identifying unit 83a ([0121]). The adaptive filter unit 83d generates an optimal cancellation signal based on the calculation result (filter coefficient) of the least squares calculation unit 83c ([0129]). The least squares calculation unit 83c calculates an optimal cancellation signal based on input signals from the basic signal generation unit 83b and the vibration sensor 29 ([0126] to [0129]).
The drive control unit 83e outputs an output signal based on an input signal from the adaptive filter unit 83d to the drive circuit 53A ([0130], [0131]). The drive circuit 53A drives the actuator 30 based on an input signal from the drive control unit 83e ([0168]).